The present invention relates to a system for storing flowable, granular materials, such as grain in large piles which may contain as much as three million bushels of the materials.
Granular materials, such as grain, are generally stored in large commercial elevators or in other permanent structures. During harvesting seasons such permanent storage facilities often times become filled and other storage facilities must be found. Sometimes the grain must be left in the open in uncovered piles thereby causing serious loss due to the elements. Other times the excess grain is stored in small temporary facilities, which may be of either rigid or collapsible construction. Typical examples of collapsible storage facilities are shown in Gardon U.S. Pat. No. 1,473,845, Wunderwald et al U.S. Pat. No. 2,731,050, Bronner U.S. Pat. No. 3,539,057, Luders U.S. Pat. No. 3,727,656, and Ptaszek U.S. Pat. No. 4,121,389.
Wunderwald and Luders both show systems where grain is piled under a flexible cover in supporting relation thereto. The covers have a central opening and are initially in a collapsed condition. The central opening is lifted, and grain is introduced therethrough to form a pile which extends downwardly from the fill point along a natural angle of repose. This angle may be in the order of about 27.degree. for wheat or 22.degree. for corn.
Wunderwald's system includes a flexible bottom portion which is attached to the cover, and the bin which is so defined is secured in place by staking down the margins prior to filling. In the system of Luders the cover is positioned upon an impermeable base. The edges of the cover are joined to the periphery of the base by an adhesive or by heat sealing. Alternatively, the cover is formed integral with the base.
The systems of Wunderwald and Luders both are limited to use for storing relatively small quantities of grain in the order of about 1,000 bushels or less. When the teachings of Wunderwald or Luders are extended to larger size storage operations it is found that the filling opening in the cover cannot be lifted to proper fill height due to the natural sagging of the cover material. For example, a 25,000 bushel pile of corn has a height of about 17 ft. and a diameter of about 84 ft. at the base. The surface area requiring coverage by the cover is about 600 sq. yd., and a suitable cover material for such an area weights over 700 lbs.
Accordingly, it may be appreciated that there has been a need for a readily erectable temporary storage facility for large quantities of flowable granular materials.